The present invention relates to tuned vibration isolators or decouplers which exhibit anti-resonant characteristics. More particularly, the present invention resides in an improved isolator having resiliently connected rotatable masses and tension or suspension cables for interconnecting two bodies which are to be vibrationally isolated or decoupled from one another.
Copending U.S. Pat. application Ser. No. 249,131 filed May 1, 1972 by William G. Flannelly now U.S. Pat. No. 3,829,052, and having the same assignee as the present application discloses a vibration isolator of the type to which the present invention relates. The isolator interconnects two bodies and exhibits anti-resonant characteristics such that vibrations at a given forcing frequency generated in one of the bodies are prevented from being transmitted to the other body. The transmissibility characteristics of the isolator are said to be of zero or low impedance because the isolator prevents or substantially reduces the level at which vibrations at the given forcing frequency are transmitted between the two bodies. The bodies are, therefore, effectively decoupled insofar as vibrations at the given frequency are concerned, but are otherwise interconnected by the isolator.
The isolator disclosed in FIG. 6 of the above referenced application employs two rotatable inertial masses that are resiliently coupled with the axis of rotation spaced in parallel relationship. Tension or suspension cables are wrapped around the rotatable masses in such manner that loads transmitted between the bodies interconnected by the cables cause the masses to roll along the cables. Vibratory loads applied in addition to the static load cause the masses to roll back and forth about a static position on the cables. If the masses and the resilient element or elements coupling the masses are properly tuned, vibrations at a given frequency are dissipated in the motions of the masses and are not transmitted between the bodies.
Vibration isolators or low impedance decouplers of this type are particularly useful in the aircraft field for suspending large bulky loads from helicopters. Stability problems associated with a suspended load, the load slings and the helicopter can result in dangerous situations with potentially catastrophic consequences if vibratory forces transmitted between the helicopter and a load reach resonance. Vertical bounce produced by such vibratory forces between a helicopter and a load is not desirable and an isolator which effectively decouples the helicopter and load in the resonant frequency band is highly desirable.
Passive vibration isolators, such as mass-spring isolators, are desirable for eliminating vertical bounce between a suspended load and a helicopter or between any other coupled bodies since they are self-contained and require no power input or feedback devices. An isolator of this type should be lightweight, small in size and effective regardless of the cargo weight, the helicopter weight and the dynamic characteristics of the slings and other equipment associated with the interconnected bodies. It is also desirable that the isolator be a low maintenance item which can be achieved by eliminating bearings, pivots, linkages and other parts having sliding or pivoting elements. It is also advantageous to eliminate fluid-operated elements which may require periodic fluid replenishment or recharging and replacement of fluid seals. It is accordingly a general object of the present invention to disclose an antiresonant vibration isolator of the type shown in the above-identified patent application and possessing the desirable characteristics described above.